Leak resistor



w. c. LINTON LEAK RESISTOR July 2, 1940.

Filed March 6, 1939 V Patented July 2, 1940 UNITED STATES PATENT orrlca V 2.20am LEAK RESISTOR Application March 6, 1939, Serial No. 260,154

'2 Claims. ((21. 201-76) The present invention relates to resistor elements and the method of making the same and .more particularly to the so-called leak resistors commonly used in connection with minature in- 5 dicating glow lamps for electrical fuses.

These miniature glow lamps contain a mixture of inert gases which pass electric currents between the electrodes thereof having a relatively .low potential difference and when the electrodes ii) are connected in series with a leak resistance, the lamps are well suited as a practical indicator for plug fuses, cartridge fuses andindicator attachments for all types of fuses, as when the fuse element becomes blown or ruptured, the resistor 15 will provide means for resisting the flow of cur rent through the circuit to which the fuse is applied for preventing damage'in the electrical circuit at the point where the short circuit occurs and yet this resistor will permit sufficient leakage of the current to.cause the lamp to glow for giving or emitting a visible signal or indication as to=the blown or ruptured condition of the fusible element.

It is common practice to form resistors from molded materials as, for example, a material containing carbon or graphite as the conductor, a fillersuch as sand, clay or other finely divided insulating materials and a non-conducting binder such as shellac, phenol-condensation products, '30 thermo-plastic products of rubber and the like, all of-which require heat, pressure, or heat and pressure-to form these moldable materials into a homogeneous mass having the required electrical characteristics. Still further, these conventional and molded types-of. resistors have to be treated with a highly conductive material or capped with bronze, brass or a combination of these metals at points where the conductors are to be connected or fastening elements are 0 required such as rivets, solder and the like for connecting the conductors to these molded t of resistors.

I have found that by mixing together powdered graphite, a powdered thermo-plasticoondensation derivative of rubber prepared by the treatment of rubber with a halide of amphoteric metal, and kaoline, that a 'moldable resinous powder is formed suitable for making leak resistances.- A similar product is obtained if 50 chlorostannic acid, or analogous compound of an amphoteric metal, is used instead of a halide of an ainphoteric metal. To render this moldable powder plastic, I add thereto a petroleum solvent which causes the rubber derivative contained 'within this powdered mixture to become plastic and this plastic rubber derivative will adhere to and holdthe plastic graphite and kaoline together in proper spaced relation so that when I the solvent completely evaporates, a resistor may be formed having the desired electrical and phy- K 'sicalcharacteristics. Before the solvent is allowed to evaporate, this plastic mass can then be molded into various shapes or sizes required. In addition to the well known chemical reactions, physical and electrical characteristics of this '10 thermo-plastic rubber derivative, it has a great affinity to all kinds of metals and, therefore, if a lead. wire of a glow lamp or other.con ductor is embedded in or attached to this plastic lmass, they will adhere thereto, thereby establishing a connection between these conductors and the resistor without the use of additional fastening elements. When the solvent is allowed "to evaporate, a hard mass results wlrichwill not break down with age and'which will bond solidly to and electrically connect the graphite to the metal conductors attached thereto or embedded therein, thereby eliminating the used heat, pressure, or heatand pressure in preparing or forming the'resulting product.

It is therefore an object of the present invention toprovide an electrical element having certain characteristics for adapting it for use in providing resistance in electrical systems or circuitswhich can be easily and readily handled; 3o molded into various shapes and sizes without heat, pressure, or heat and pressure, have a great aflinity towards all kinds of metals and one which when molded or shaped into its final form bonds solidly, will not break down with age, repels water and moisture, and will resist heat to a degree beyond itsLoperating temperatures to which it is suited, that is, a leak resistance for electrical indicating fuses.

Other objects of the invention will be in part obvious and in part pointed out hereinafter. Y Fig. l is a vertical sectional view of an indicating plug fuse having my leak resistor applied thereto, and

Fig. 2 is an enlarged illustration in side elevation of one form of my leak resistor, having a portion thereof broken away and conductors connected thereto.

In carrying out my invention, I employ as a binder for the resistor a fine, sand-like powder or an un-milled form of a thermo-plastic condensation derivative of rubber prepared by the treatment of rubber with a halide of an amphoteric metal or chlorostannic acid which during its preparation is formed into an emulsion u I and thereafter steam distilled with agitation to remove the solvent contained therein whereby the same precipitates as a fine, sand 'like themeplastic resinous powder.

I also employ a comminuted conductive material such as powdered graphite, and an inert material as a filler such as haoline. which is a very pure, white clay ordinarily obtained in the form of an impalpable powder. These powdered ma= terials are extremely fine so that no grit can be perceived by touch and arethoroughly mixed ture may be left in this ,Ldry, powdered state until it is desired to form the same into resistor elements.

In forming the resistor elements, this powdered mixture may be deposited in a recess or other cavity formed in the casing of electrical fuses or other supports to which the resistor elements are to be applied. To this dry, powdered mixture, I add a high grade petroleum solvent by dropping the same thereupon until this powdered mixture becomes thoroughly saturated with the solvent, causing a resulting plastic mass. Lead wires or other conductors may then be inserted or embedded within this plastic mass or retained against the same. When the solvent is allowed to completely evaporate, a resulting solid mass is formed having the-lead wires or conductors permanently attached thereto.

These resistor elements may also be placing a quantity of this powdered mixture ,in a

bowl or other container and then mix the same with a petroleum solvent until a plastic mass is formed. Before the solvent is allowed to evaporate from this plastic mass, small parts thereof may be taken from the bowl or other container and formed into the resistor element of the required size or shape or; this plastic mass may be placed within a closed container to prevent the solvent from evaporating, and such container having a suitable ejecting device whereby small portions of the plastic mass may be dispensed therefrom as needed. Small parts of this plastic mass may be applied to the opposing ends of lead wires or other conductors where a resistor element is required betweenithe same and when the solvent contained within this plastic mass evaporates, thelead wires or conductors will be connected together and retainedin spaced relation. Also, a small part of this plastic mass maybe placed about the ends of a lead wire-or other conductor and when the solvent evaporates.

this plastic-mass will adhere to the lead wire.

Thlsdrymassmaythenbesimplyplaoedazainst another lead wire or. othcr conductor, thereby g a leak r between such-condoctors.

The solvent employed is preferably benzene or toluol but other well known ooal'tar derlvatlv or petroleum solvents maybe used.-

ture containing one part of the theme-plastic resinous binder, one part of graphite and two parts of kaoline will have an electrical resistance .rating' of 50,000-0hms or more or suflicient reformed by' Leakresistorsprepared'fromapowderedmixy circuit of 110 volts that will prevent any appreciable amount of current from passing through the circuit, but when a glow lamp indicator is connected to this circuit, the resistor will pass an infinitesimal amount or sufllcient current to keep the lamp glowing. These lamps will function in electrical circuits of 110 volts having a resistance rating of anywhere between 50,000 and 650,000 ohms as electric power required to operate these lamps maybe as low as .02 of 9. watt. Therefore, the resistors made from the above powdered mixture in the proportions as above enumerated need not all have the same constant rating, but the conductivity of the powdered mixture may be accordingly determined, over a wide range, by the proportion of the graphite employed. By thoroughly mixing this dielectric thermo-plastic resinous powder with a comminuted conductive material, particles of this mixture are caused to distribute themselves quite uniformly throughout the mass, with at least a part of them in con- The electrical resistance ratings of my resistor may be increased by reducing the amount of graphite and the'amount of graphite removed can be replaced with kaoline'. Obviously when applying a glow lamp indicator and resistor to high potential circuits, less graphite should be used and I have found'that a mixture containing approximately 15% graphite, 25%. the thermoplastic resinous binder and kaoline will produce resistors suitable for electrical circuits of 220 volts and a mixture containing 10% graphite, 25% the thermo-plastic resinous binder and kaoline is required of resistors applied toelectrical circuits of 660 volts. My method of preparing these leak resistors will obviously cause all succeeding resistors to greatly vary in their electrical resistance ratings but yet when using the same' with indicator glow lamps for fuses, the resistance and lamp will properly function over a wide range when preparing the resistors from a powdered combination in about the proportions above mentioned.

In the drawing, I have illustrated in Fig. 1 thereofan electrical indicating plug fuse as is more particularly described in my copending application Serial No; 260,155, filed March 6, 1939,

which comprises a casing I having a central contact 2 and a threaded contact shell 3 secured thereto. Within theexplosive chamber of this casing is a fusible link 4 which is connected in of thisleak resistor will contact with the inner face of the threaded metallic contact shell 3. 'A

glowllamp i is also provided within the casing I which is utilized for designating the blown or. ruptured condition of the fusible element I. --This lamp has one of its lead wires "I connected to the central contact'terminal 2 and its other lead wire 8 is embedded within the leak raistor 5. From this arrangement, it will be obvious that whereas the fusible element or link I is con- 7 .nected to the contact terminals 2 and 3, the lamp 6 and resistor 5 are also connected in series with. the contact terminals 2 and 3 but in parallel to the fusible element 4, whereby when the latter blows, due to a short circuit within the electrical system to which the fuse is applied, the current will be directed through the lamp and leak resistor, thereby causing the lamp to glow. The lamp or leak resistor is never rendered operative until after the iusible link is blown and as these leak resistors have a resistance rating or anywhere between fifty thousand and fifteen million ohms, considerable heat is generated therein after the blowing of the fusible element and when current is first supplied to the lamp 6 for causing the same to strike or glow.

In applying my leak resistor to this type of indicating plug fuse, I first thoroughly mix together kaoline, graphite and the resinous binder in dry, powdered form. This dry, powdered mixture can then be deposited within the opening or recess formed within the casing l of the fuse until the powder comes in direct contact with the inner face of the shell 3. After this powdered mixture is in direct contact with the threaded shell 3, a few drops of benzene is applied to the mixture, wherein it becomes plastic. The lead wire 8 of the lamp is then inserted within this plastic mixture and when this solvent evaporates, the mixture results in a solid, flexible mass which strongly adheres to, the metallic conductors 5 and 8, thereby establishing an excellent mechanical and electrical connection between the two conductors, which will not break down with age or in any manner become impaired should excessive heat be later applied to the leak resistor as again would render the same plastic..

In Fig. 2 of the drawing, I have illustrated another form of preparing my leak resistor in which this dry, powdered mixture of kaoline, graphite and, resinous binder is first subjected to a solvent I such as benzene until it forms a plasticmass.

'Ihis'plastic mass may then be further formed into any shape or size desired. While this resistor is in this plastic state, a lead wire 9 may have one end embedded therein or a flat contact terminal l0 may be placed thereagainst, whereby when the solvent within this plastic mass evaporates, these metallic contacts 9 and ID will strongly adhere thereto, forming an excellent mechanical and electrical connection without the aid of any mechanical or other 'forms of fastening or connecting elements.

Should this leak resistor be subjected to heat or temperatures above 200 F. it will soften and, yet remain in a bonding contact with the metallic. conductors. When the heat is removed 'and the resistor allowed to again cool, it will still retain its desirable electrical and mechanical qualities. A resistor, after once being formed in the shape and size desired, may be softenedby. applying a solvent,'such as benzene'thereto, whereby conductors may beinserted therein or placed in contact therewith. when the solvent is allowed to evaporate, the metallic conductors will be retained in a bonding contact therewith.

manifestly, the construction herein shown is capable of considerable modification and such modifications as come within the scope of my claims, I consider within the spirit'of my invention.

I claim: 1. A leak resistance element comprising a homogeneous mixture composed of graphite, an unmilled powdered form of a resinous reaction product comprising a thermo-plastic condensation derivative of rubber prepared by the treatment of rubber with a halide of an amphoteric metal or chlorostannic acid, and powdered kaolin, said resinous product being uniformly dispersed throughout the other materials.

2. A- leak resistance element comprising a homogeneous mixture composed substantially of one part powdered graphite, a substantially equal part of unmilied powdered form of a resinous reaction product comprising a thermo-plastic condensation derivative of rubber prepared by the treatment of rubber with a halide of an amphoteric metal or chlorostannic acid, and powdered kaolin, said resinous product being uniformly dispersed throughout the other materials.

3. The subject matter of claim 2, and a metal conductor element in intimate contact with said homogeneous mixture and completely adherent thereto.

4. A leak resistance element comprising a homogeneous mixture composed substantially of one part powdered graphite, a substantially equal part of unmilled powdered form of a resinous reaction product comprising a thermo-plastic condensation derivative of rubber prepared by the treatment of rubber with a halide of an .amphoteric metal or chlorostannic acid, and substantially two parts powdered kaoline, said resinous product being uniformly dispersed throughout the other materials. 7

5. The method of fabricating leak resistance elements which consistsin mixing together powdered graphite, kaolin, and a resinous reaction product comprising a thermo-plastic condensation derivative of rubber prepared by the treat- 'ment of rubber with a halide of an amphoteric metal or chlorostannic acid, saturating said mixture with a cold hydrocarbon of the benzene type to form a plastic mass, applying the saturated plastic mass without pressure to the situs where the resistance element is required, and allowing the hydrocarbon to evaporate.

6. The method of fabricating leak resistor elements and attaching metallic electrical conductors thereto which consists in mixing together powdered graphite, kaoline and a thermoplastic condensation derivative of rubber pre-' pared by the treatment of rubber with a halide of an'amphoteric metal or chlorostannic acid, saturating said powdered mixture with a cold hydrocarbon of the benzene type to form a plastic mass, placing the metallic electrical conductors in intimate contact with said saturated plastic mass and allowing the hydrocarbon to evaporate whereby the metallic electrical conductors will be completely adherent thereto.

'7. The method of fabricating leak resistance elements and attaching metallic electrical conductors thereto which consists in mixing together powdered graphite, kaoline and an unmilled thermo-plastic condensation derivative of rubber with a halide of an amphoteric metal or chlorostannic acid, applying said powdered mixture tothe situs where the resistance element is required, saturating said mixture with a cold hydrocarbon of the benzene type to form a plastic mass, inserting a metallic electrical conductor within said WILLIAM C. L'IINTON.

plastic mass, and allowing the hydrocarbon to evaporate. 

